This invention relates to a vehicle body structure having a front side member constituting a portion of a front body frame. More specifically, the total height of the front side member is increased by drawing sheet metal to form a plurality of longitudinal reinforcing members having substantially hat shaped cross-sections and vertically stacking the members.
As shown in FIG. 10, a front side portion of a vehicle body 1 of an automobile is provided with a front side member 11 extending in the longitudinal direction of the automobile. The front side member 11 constitutes a part of a frame of a front of the vehicle body, and it usually has a front end thereof supporting a front bumper, etc., an intermediate part thereof receiving an input of a suspension, and a rear end. The front end of the front side member 11 is positioned at the side of an engine compartment 2, and the rear end of the front side member 11 extends from a bottom of a dash panel or firewall 21 to a lower surface of a front part of a floor panel 22.
FIG. 11 is a perspective view showing an example of a conventional front side member 11 (the one at the left side of a vehicle body). As shown in FIG. 11, the front side member 11 is comprised of a side member front part 12 and a side member rear part 13, which are joined together at a joint 14. The side member front part 12 is usually formed to have a rectangular closed cross-section. The side member rear part 13 cooperates with the fire wall 21 and the floor panel 22 to typically form a rectangular closed cross-section. Reference numeral 13a denotes a flange portion that joins the side member rear part 13 to the respective lower surfaces of the fire wall 21 and the floor panel 22.
A reinforcement 31 is mounted at a position where the side member front part 12 receives the input of the suspension (as indicated by the diagonal lines) in order to ensure a sufficient rigidity to resist the input of the suspension.
On the other hand, the side member rear part 13 joined to the bottom of the fire wall 21 must have sufficient rigidity in order to prevent the bottom of the fire wall 21 from deforming in the event of a crash of the vehicle. To improve the rigidity, the cross-section of the side member rear part 13 is preferably enlarged (in particular, an area joined to the fire wall 21 is enlarged). In terms of machining, however, it is difficult to simply enlarge the cross-section of the side member rear part 13. Therefore, under the present circumstances, a second reinforcement 32 is added to the interior of the side member rear part 13 to ensure the rigidity as shown in FIG. 12. FIG. 12 is a cross-sectional view taken perpendicular to an arrow Cxe2x80x94C in FIG. 11.
More specifically, the side member rear part 13 is usually formed to have a substantially hat-shaped cross-section that is opened upward (toward the fire wall 21) as shown in FIG. 12 so that it can be joined to the bottom (at the outside of a vehicle compartment) of the fire wall 21. A flange portion 13a at the upper opening side is joined to the bottom of the fire wall 21.
Such a reinforcing member, having the substantially hat-shaped cross-section, is formed by drawing of a metal sheet member. However, an increase in the drawing depth D of the reinforcing member (see FIG. 13) (usually, the increase in the ratio of the drawing depth D to the width W, i.e. D/W) makes the drawing process more difficult. In particular, the increase in the board thickness of sheet metal material makes it difficult to draw the reinforcing member in an increased drawing depth D (deep drawing). In the case of the side member rear part 13, the sheet metal material must be thick due to the necessity of ensuring sufficient strength and rigidity, and the width W thereof is restricted in terms of the arrangement with the other vehicle components. This results in the restriction on the drawing depth D.
Accordingly, as shown in FIG. 12, the reinforcement 32 is added to the interior of the side member rear part 13 to ensure rigidity.
Therefore, the cross-section of the side member rear part 13 opened toward to the fire wall 21 (i.e. the total height of the side member rear part 13) H is restricted according to the drawing depth D.
Incidentally, increasing the total height H of the side member rear part 13 is the most efficient way to prevent the deformation of the fire wall 21.
There is space below the side member rear part 13, but the wheel well is provided there. Therefore, in terms of the space, it is not possible to extend the side member rear part 13 and the rear part of the side member front part 12 downward to increase the total height H.
In view of the above, it would be desirable to provide a vehicle body structure that increases the total height of a front side member to efficiently improve the rigidity of a front side member to prevent deformation of the fire wall.
The invention provides a vehicle body structure that improves rigidity by utilizing a longitudinal front side member of a vehicle body frame which includes a front part which extends from a front bumper to a joint and a rear part which extends from the joint to a firewall and a floor panel. The rear part includes stacked longitudinal reinforcing members, each member having a substantially hat shaped cross section which includes two sides and a bottom, an overlap margin where an uppermost portion of the sides of one longitudinal reinforcing member is coupled to a lowermost portion of the sides of another overlying reinforcing member, a drawing depth of each member which is measured perpendicular to the bottom of each member, and a total height which equals a sum of the drawing depths of each member minus the overlap margin between each of the members.
More specifically, the reinforcing members having the substantially hat-shaped cross-sections can easily be formed by drawing of sheet metal members, but the drawing depth equivalent to the height of the substantially hat-shaped cross-section is restricted in the case of the drawing. In particular, since the front side member is made of a rigid sheet material with a great board thickness, it is impossible to increase the drawing depth D of the members having the substantially hat-shaped cross-sections (i.e. the height of a part joined to the fire wall). On the other hand, in the vehicle body structure according to the present invention, the plurality of reinforcing members are stacked on the fire wall, and therefore, the height of the front side member is increased according to the sum of the drawing depths or height of the stacked reinforcing members less the joint margins of the reinforcing members.
Therefore, the part of the front side member joined to the fire wall is increased in height while the reinforcing members are machined by a drawing process, which can easily be performed with excellent machinability although the drawing depth is restricted. It is therefore possible to increase the total height of the part of front side member joined to the fire wall to efficiently improve the fire wall supporting rigidity without raising the component manufacturing cost or the like.
The improvement in the rigidity of the front side member surely prevents the fire wall from deforming in the event of a vehicular crash.